It is necessary to determine nitrogen in a sample in chemical or laboratory testing circumstances. This is also useful in batch or continuous process control. Such circumstances often call for determination of an output of total bound nitrogen in a particular sample. The term "bound nitrogen" refers to nitrogen which is a chemical constituent of a compound as opposed to free nitrogen. Free nitrogen or diatomic nitrogen, typically found in the atmosphere or disclosed in a sample, is compounded only with the most difficult of efforts; in fact, nitrogen in the atmosphere can be viewed practically as an inert gas which is evidence by the difficulty of reacting diatomic nitrogen with a compound. It is often important to analyze the total nitrogen content of one or more compounds in a sample or specimen where the nitrogen content is important but unknown. This type of measurement can be provided by the equipment and procedure which are set forth in Parks, et al. which is U.S. Pat. No. 4,018,562. In many instances, that analysis is more than sufficient. In other instances, it is important to have an additional break down of the nitrogen content. In other words, a representation that nitrogen represents 100 ppm may be adequate in some circumstances, but in other circumstances, the data must be broken down into specific nitrogen compounds, for instance, nitrites and nitrates are indicated separately. The present disclosure sets forth a method and apparatus for measuring nitrogen constituents in a sample and in particular for providing an indication separating the nitrite component and the nitrate component. In addition, constituents are separated into the most desirable or important nitrogen compounds from the point of view of application and use. Several examples will make this more readily apparent. Consider as one example the analysis of surface water which has washed off a large land area involving farming and ranching. The surface water discharge may carry fertilizer constituents in it. It may be very important to determine the break out of the constituents so that better control of the fertilizer application on the surface area can be executed. In this example, it may be very important to know the nitrate (NO.sub.3 -) concentration, and to also know the total nitrogen concentration. In another example, a chemical leaching process may discharge waste effluent with nitrites (NO.sub.2 -) up to a certain specified quantity. This can be tested again by use of the present method and apparatus.
One aspect of the present method and apparatus is that it avoids the wet chemistry approach which has been traditionally known as the Kjeldhal analytical procedure. The Kjeldhal method is inherently time consuming to execute and is relatively expensive. It may also create undesirable waste products. The method of the present disclosure is not a wet chemistry procedure, contrasting with Kjeldhal, and can be executed in a straight forward fashion to provide substantially no waste discharge.
Previously known methods do not provide the desirable procedure of the present disclosure. Several methods are therefore given in the following documents:
1) Nitrogen, Nitrate-Nitrite. EPA Method 353.3 (Spectrophotometric Cadmium Reduction) Storet No. Total 00630, 1974.
2) Nitrogen, Nitrate-Nitrite. EPA Method 353.2 (Colorimetric, Automated, Cadmium Reduction) Storet No. Total 00630, 1978, 1974, 1971.
3) Standard Methods for Examination of Water and Waste Water 14th Ed., 1975. 419 LC. Cadmium Reduction Method (Tentative).
4) P. G. Brewer and J. P. Riley, "The Automatic Determination of Nitrate in Sea Water". Deep-Sea Research, 1965, Vol. 12, page 765.
5) Robert D. Cox, "Determination of Nitrate and Nitrite at the Parts per Billion Level by Chemiluminescence". Anal. Chem. 1980, 52, 332-335.
6) Robert C. Doerr, Jay B. Fox, Jr., Leon Lakritz, and Walter Fiddler, "Determination of Nitrite in Cured Meats by Chemiluminescence Detection". Anal Chem. 1981, 53, 381-384.
7) James E. O'Brien and Janece Fiore, "Automation in Sanitary Chemistry--Parts 1 and 2".
8) F. A. J. Armstrong, C. R. Stearns, and J. D. H. Strickland, "The Measurement of Unwelling and Subsequent Biological Processes By Means of the Technicon Autoanalyzer and Associate Equipment". Deep-Sea Research, 1967, Vol. 14, pages 381-389.
9) C. Garside, "A Chemiluminescent Technique for the Determination of Nanomolar Concentrations of Nitrate and Nitrite in Seawater". Marine Chemistry, 11 (1982), pages 159-167.
10) A. Henriksen and A. R. Selmer-Olsen, "Automatic Methods for Determining Nitrate and Nitrite in Water and Soil Extracts". Analyst, May, 1970, Vol. 95, pages 514-518.
11) Ted W. Walsh, "Total Dissolved Nitrogen in Seawater: a New-High-Temperature Combustion Method and a Comparison with Photo-Oxidation". Marine Chemistry, 26 (1989), pages 295-311.
12) ASTM Designation: D 1254-67 (reapproved 1974). Standard Methods of Test for Nitrite Ion in Water.
As a generalization, the procedures above do not provide either total nitrogen or constituent break outs from the total nitrogen. To the extent that they do provide either nitrate measurement only or nitrite measurement only, they are unable to provide the total bound nitrogen output.